1. Field of the Invention
The present invention relates to a technique for sensing the presence or absence of an object or the state of an object.
2. Description of the Related Art
In recent years, a system has been developed in which a wireless sensor is caused to sense the presence or absence of an object or the state of an object indoors or outdoors, and a control is performed on the basis of a result of the sensing. For example, in Japan Unexamined Patent Publication No. 2004-515757, it is disclosed that wireless sensors are located in a building, and air conditioning or lighting in the building is controlled on the basis of a result of sensing by the wireless sensors, that wireless sensors are located in a home and used for security, and that wireless sensors are located on a road and used for traffic safety.
However, since a conventional wireless sensor needs a battery to operate, it is necessary to periodically replace the battery of the wireless sensor. Therefore, if a system employs a lot of wireless sensors, a high degree of maintenance of the system is required.
The present invention has been made with a view to addressing the problem discussed above, and provides a technique for sensing the presence or absence of an object or the state of an object indoors or outdoors while requiring little maintenance.